Organosilicon polymers containing the structure ##EQU2## and copolymers of these with II R.sub.2 SiO siloxane units are shown in U.S. Pat. Nos. 3,542,830 and 3,647,740. The entire disclosure of said patents being incorporated herein by reference. Those polymers containing substantially only I type units have excellent reversion resistance (i.e. they do not depolymerize when subjected to heat in confined space) as compared with polymers containing II type units. However, the brittle point of polymers made up of I type units is in the range of about -21.degree. to -25.degree.F. (29.degree. to -31.degree.C.), whereas the brittle point of polymers made up of II type units can be in the range of -80.degree.F. (-62.degree.C.) or below. Consequently, although the I type polymers have better reversion resistance, their operability is limited to a narrower temperature range than conventional organopolysiloxanes. For that reason, it would be highly desirable to produce polymers which have in combination the high reversion resistance of the heretofore known I type polymers and superior low temperature flexibility. It has been found that this can be accomplished by producing polymers of the particular structure claimed below.
It is the object of this invention to provide polymers which give the best combination of low temperature properties and reversion resistance without sacrificing high temperature stability and solvent resistance of the heretofore known type I polymers.